Julianne Moore stars in this supernatural horror film as second-generation forensic psychiatrist Dr. Cara Jessup, whose career as an expert witness has been largely built on her firm testimony that so-called "multiple personality disorder" is a hoax or a myth -- and does not really exist. Over six killers have been convicted and sentenced to death based on her assertions, though Cara has remained firm in her beliefs, both about science and about God. All of those beliefs are shaken to the core, however, when her own husband is murdered, and her father introduces her to his own most challenging patient, a troubled young man named Adam -- who would seem to suffer from multiple personalities, each of which are the identities of murder victims. Soon, Cara is in a race against time to discover whether all her convictions have really been called into question or if she is merely a pawn in a psychotic, deadly game.